Photographic exposure meter



AprilZ, 1940; v J. M. Blue 2,195,640

,PHOTOGRAPHIG EXPOSURE METER Filed July l 1938 .g INVENTOR.

sa /1 fix 4% ATTORNEY.

Patented Apr. 2, 1940 UNITED STATES PATENT orricr.

rno'roemrmc sxrosum Joseph M. Bin, New York, N. I. 7 Application July 1, 1938,'8e;ial1No. arose In Germany March A more specific object of the invention isto provide an exposure meter of the optical'type which can be read instantly without .the necessity of adapting the user's eye to existing average light conditions and which enables an'immediate 16 conversion of 'a read. scene or object brightness into photographic exposure data without removing the meter from thereading position.

Another object is to provide-an exposure meter of the type to be held at a' distance from the o user's eye in the reading position, whereby the viewing direction is substantially different from the direction of the scene or object to be photographed.

A further object is the provision of an exposure meter enabling a direct reading and/orv exposure adjustment without requiring any intermediary calculation or conversion.

Further details and objects of the invention will appear as taken with reference to the accompanying drawing forming part of this specification and wherein Figure 1 is an isometric view of a preferred construction of an exposure meter according to the invention, 4 Figure 2 is an enlarged top view of the meter according to Figure 1 showing the details of the calculator for converting a read scene brightness into exposure data for a photographic camera,

meter taken on line 3-3 of Figure 2,

Figure 4 is an enlarged isometric view similar to Figure l with the upper part'of the meter removed, 1

Figures 5, 6 and 7 illustrate forms of construction of the optical wedge embodied in the meter according to the invention,

- Figure 8 is a graph illustrating the construction of the optical wedge.

Like reference numerals are 'used to denote like parts throughout the different views of the drawing.

Referring more particularly to Figures 1 to 4,

the improved exposure meter shown comprises substantially a fiat rectangular casing having the following description proceeds Figure'3 is a longitudinal cross-section of the (01- 88-23) a lower half ll and an upper half i! made of any suitable material preferably a condensation product of the phenolformaldehyde type known by the trade name "Bakelite" or an equivalent moldable and fixable material. The two' halves II and II are connected in any suitable manner such as by means of screws III as shown in Figure 3. In one of the shorter end walls of the casing there'is mounted a plate l2 of light pervious material such as frosted glass, Celluloid, 1 cellulose acetate, or an-equivalent material to enable the entrance of light rays reflected from a scene or object field to be photographed towards which the meter is pointed in the reading position. At a suitable place between the-plate 15 I2 and the opposite end wall and the casing there is placed an optical wedge member l3 substantially parallel to the plate l2, whilea mirror or equivalent reflecting member I4 is mounted at the opposite end of the casing serving to deflect m the light rays passing the wedge member i3 at an angle preferably a right angle, that is in a vertical or upward direction towards the eye of .an observer in the reading or horizontal position of the meter. Plate 12 and wedge member i3 may be held in position in any suitable manner such as within grooves as shown in the drawing. The optical wedge i 3 in the example illustrated comprises a plate to which are applied a series of numbers, letters or other marks and having 30 a transparency or opacity varying gradually or step by step from one end to the other. One simple way of making such a wedge consists in providing a pair of plates of glass, Celluloid, or the like, one of which plates (l3a according to 35 Figure 5) istransparent and has applied thereon opaque or dark numbers or marks, etc.,- while the second plate (I317 according to Figure 6) superimposed upon the plate l3a forms an optical wedge having'an opacity or transparency in- 40 creasing gradually or in steps from one end to the other according to a desired law orrelationship. In this manner, by superimposing the plates I 3a and 131) which may be connected together such as by gluing, riveting or in any 4 other suitable manner, there is obtained a composite plate with dark marks such as numbers or letters appearing against a background of gradually increasing opacity from left to right as shown in the example illustrated. 50

Another way of constructing a wedge, suited for the purpose of the invention is to cover the plate l3a with a number of sheets or plates 130, Figure '7, of substantially like opacity but of successively decreasing length to obtain a staggered composite wedge member with a similar efiect to the preceding example as will be readily understood.

In a preferred alternative construction of the Nb or ltd there will appear upon the mirror 14,

in the example illustrated, a series of numbers or marks-of gradually increasing opacity from left to rightupon a dark background as is readily number nor is there any unnecessary delay in acunderstood.

In the example illustrated, the numbers applied to the wedge I! which are characteristic of the object field to be reproduced in .a camera, the wedge I3 is arranged at a suitable distancefrom the end of the casing or the plate l2 to form a channel or light baflle in such a manner that the effective field angle a, Figure 3, substantially corresponds to or is somewhat less than the average field angle of photographic cameras. In this manner the inclusion of light rays coming from objects outside the object field to be reproduced in a camera is substantially avoided such as the light from a bright sky which would cause erroneous exposure results. In order to shield the mirror H to prevent reflected and disturbing side light from interfering with the proper reading, there is provided a hinged bafile or shield or light value" is to be determined and by viewing the mirror H as shown in Figure l, a series of numbers will be observed in the example i1.- lustrated the diaphragm or stop members f0.4 to I16 of or upon a background of gradually increasing opacity. The arrangement and design of the meter is such that the number which can just be ascertained or read with ease is characteristic' of the existing scene brightness and it becomes the further object to convert this read number of scene brightness or light value into suitable exposure data for a photographic camera to obtain a well exposed picture.

It will be appreciated that the method of reading a scene or object brightness in the manner described has great advantages over the methods used with'meters based on a similar principle. On the one hand, no mechanical adjustments are required in operating the optical wedge until the appearance or disappearance of any mark or commodating the, observer's eye each time before taking a measurement by firmly holding the meter close against the eye. In using the meter according to theinvention the reading can be carried out instantly and the value read converted into proper exposure data without changing the position of the meter. The invention is further distinguished from meters of the type to be held at a distance from the user's eye in the reading position in, which case direct rays from the scene or interfering lateral or reflected light may greatly interfere with the accuracy and proper reading. In using the meter described by the invention, this diificulty is'substantially overcome by viewing the meter in a direction different from the direction of the scene or object to be photographed. 1

Referring to the calculator for translating. a measured light value into photographic exposure data the same is mounted on the same .face of the casing carrying the hinged cover 5 and is constituted by a conversion scale device comprising substantially three different types of scales two of which are fixed, while the third is adjustable relative to the meter casing. The latter adjustable scale in the exampleshown at I! is of annular shape and arranged in a corresponding annular depression or guide groove in the top face of the cover ii. This rotatable scale has graduations I 8 similar to those of the wedge l3, 1. e. stop or diaphragm numbers from f1 to 64 in the example shown including the stop numbers on the wedge I 3. The scale I! is held in place by a cover plate I! having a 'circular opening with its inner diameter adjacent to the-outer diameter of the scale l8 on.the rotatable member II. The plate I9 is fixedly secured to the casing by means of screws or the like and carries a sector shaped'scale 20'calibrated in film or plate speed numbers according to the well known "Scheiner or any other system, said scale being adjacent to and cooperating with the stop or light value scale l8 on the rotatable member l1.

Scale I! is thus guided within the annular depression in the upper face of the cover Il and may be rotated relative to scale 20 for which purpose its outer edge is milled or knurled and the casing provided with suitable recesses at both sides in such a manner that the lmurled edge of the disc. l1 projects beyond the plate l9. Thus, if the meter is held in the palm of the hand, the thumb readily falls into position for turning the disc l1, whereby both reading and conversion may be carried out without changing the position of the meter.

'Ihereis further provided a third central disc shaped scale member 2| secured to the top face of the cover ll partly overlying the rotatable arranged adjacent to the inner edge of the scale l8 of the member i I. The member 2| carries a scale 22 calibrated in shutter speeds. There are provided a pair of further scales 23'and 24 also calibrated in shutter speeds" and arranged upon the member 2| concentrically with the first shutter speed scale 22. Each of the three shutter speed scales 22, 23 and 24 serves for use under difierent general light conditions to compensate for the difference in the average sensitivity or acuity of vision of the human eye. Thus, the outer scale 22 in the example shown corresponds to outdoor objects or scenes in bright daylight or sunshine. The scale 23 applies to scenes on heavily clouded days without sunshine or to light interiors. The inner scale 24 applies to night scenes or dark interiors, dense woods,

majority of photographic objects while the use of the remaining scales may be acquired by a short practice in a simple and easy manner. In the example shown, the numbers on a simple hatched background represent fractions of a second, those on a white backgroundrepresent seconds and those on a double hatched background represent the minutes in accordance with standard practlce.

The design of the optical wedge may be such that the opacity varies linearly either gradually or in steps from one end to the other such as shown by the graph in Figure 8 (line A). In this case, by the proper design of the scales 22 to 24 it is possible to correct for the different acuity of vision or sensitivity of the human eye under different average light conditions as pointed out hereinabove. According to a modification, the wedge l3 may be designed according to a nonlinear law to compensate for the fact that the human eye is capable of discerning relative differences of brightness more easily under low average light conditions than in strong lights. The opacity of the wedge may vary accordingto a curve such as shown in B in Figure 8 which theoretically follows an exponential law. If a wedge constructed in this manner is used, it may be possible to dispense with the additional shutter speed scales or the latter may be additionally employed to compensate for different acuity of vision for diiferent average light conditions.

In use the meter is pointed towards the object or scene to be photographed as shown in Figure 1 with the cover [5 raised to expose the stop figures on the graduated wedge at the bottom of the reading slot. As pointed out, this cover in the raised position serves as a shield or guard against front light for convenience and greater accuracy of readingl In the reading slot there will appear as many of the light values or stops from 1.4 to 16 in the example illustrated as correspond to the brightness of the object; Starting from the highest figure, the user then decides which is the dimmest or faintest stop number that is readable without effort. By then rotating the stop scale I! of the calculator until the faintest figure read in the reading slot is opposite the proper speed of the film used on the scale 20, all stops are aligned with the corresponding exposure times or shutter speeds on the inner scales or time circles 22, 23 and 24. The choice of the proper time circle depends on the type of illumination under which the observer reads or the acuity of vision as described hereinabove.

As will be understood, the stop and shutter speed scales may be mutually exchanged with out substantially affecting the operation and results obtained. The provision of stop numbers on the optical wedge in place of special light value numbers or marks greatly simplifies the construction and the operation of the device as is understood from the above. A further'advantage of using exposure figures such as stop numbers as brightness marks on the graduated wedge, besides dispensing with a special brightness or light value scale is the fact that in this manner it is possible to use the meter without the conversion device or calculator by employing a definite exposure time for a given film speed. 'Thus, referring to Figure 2, it is seen that by employing an exposure time of ,4," second and a film'having a speed number 23 or any other correlated exposure time and film speed numbers appearing opposite each other on the scales and 24, the figures read in the reading slot represent the proper stop or lens diaphragm settings under the chosen conditions. Since the films generally used at present have speeds ranging from about 20 to 26 Scheiner and the exposure time and shutter speeds for the majority of subjects are from to of a second, it is seen that in this manner the exposure meter according to the invention affords an instantaneous determination of the proper exposure values without the necessity of operating any movable elements for the great majority of cases under average light and picture taking conditions.

It will be evident from the above that the invention is not limited to the specific details and constructions shown herein for illustration, but that the invention is susceptible of numerous embodiments and variations coming within its broad scope and spirit as defined in the appended claims. The specification-and drawing are accordingly to be regarded in an illustrative rather than a limited sense.

I claim:

1. In a visual photographic exposure meter, the combination of a light meter unit comprising a casing having a pair of openings defining a light passage therebetween, the first. of said openings being provided in the front wall and the second opening being provided in the top wall of said casing near .the rear edge thereof, an optical wedge element located within said casing at an intermediate point between said openings, said wedge element having a series of scene brightness marks thereon of gradually increasing opacity, a light-deflecting device located within said casing adapted tov deflect light rays entering the first opening and passingsaid wedge in a direction towards said second opening whereby, by holding said casing with said first opening facing a'photsgraphic scene, the brightness mark being just readable by viewing said wedge through said second opening is characteristic of the scene brightness to be-determined. under a given average light condition, and a converting unit mounted upon the top wall of said casing adjacent to said second opening for translating a read scene brightness into appropriate photographic exposure data,

said converting unit having relatively adjustable scale memberscalibrated in exposure determining values for a photographic camera, one of said scale members having a series of marks thereon arranged to be set in accordance with the brightness mark read on said wedge element, and

' identical to those on said wedge element and being another of said scale members having a plurality of adjacent identical staggered scales each of the staggered scales being designed for use under a different principle average light condition,

2. In a visual photographic exposure meter, the combination of a light meter unit comprising acasing having a pair of openings defining a light passage therebetween, the first .of said openingsbeing provided in the front wall and the second opening being provided in the top wall of said casing near the rear edge thereof, an optical wedge element located within said casing at an intermediate point between said openings, said wedge element having a' plurality of marks thereon of gradually increasing opacity representing a consecutive series of exposure values for a photographic camera, an inclined mirror located within said casing opposite said. second opening whereby, by holding said casing with its front opening facing a photographic scene the mark being just readable by viewing said wedge through said second opening and mirror is characteristic of the scene brightness to be determined under a given average light conditon, and a converting unit mounted upon the top wall of said casing adjacent to said second opening for translating a read scene brightness into appropriate photographic exposure data, said converting unit comprising a first adjustable scale member having a series 01' exposure marks thereon identical to those on said wedge element and arranged to be set according to the mark read on said wedge, and a second relatively fixed scale member calibrated in coordinated camera exposure values, said last mentioned scale member having a plurality of ad-.

jacent identical staggered-scales, each of said staggered scales being designed for use undera different average light condition in cooperation with the first mentioned scale member.

3. In a visual photographic exposure meter, the combination of alight meter unit comprising a casing having a pair of openings defining a light passage therebetween, the first of said openings. being provided in the frontwall and the second opening being provided in the top wall of said casing near the rear edge thereof, an opticalwedge element located within said casing at an intermediate point between said openings, said wedge, element having a plurality of marks comprising a consecutive series of stop numbers age light conditiom'and a converting unit mounted upon the top wall of. said casing adjacent to "said second opening for translating a read scene brightness into appropriate photographic exposure-data, said converting unit comprising a first adjustable scale member having a series of "stop markings thereon identical-to those on said wedge element and arranged to be set according to a mark read on said wedge, and a second relatively fixed scale member arranged in cooperative relation to the first scale member calibrated in coordinated shutter speed values, said last scale member having a plurality 01' adjacent identical staggered scales, each of said staggered scales designed for use under a diflerent average light condition.

4. In an exposure meter as claimed in claim 2, a third scale member calibratedin emulsionspeeds and arranged to cooperate with a mark of said first scale member;

5. In a visual photographic exposure meter, the combination of a light meter unit comprising a casing having a pair of openings defining a light passage therebetween, the first of said openings being provided in the front wall and the second opening being providedin the top wall oi said casing near the rear edge thereof, an optical wedge element located within said casing at an intermediate point between said openings, said wedge element having, a plurality ofmarks thereon representing a consecutive series of exposure values for a photographic camera'of gradually increasing opacity, an inclined. mirror located within said casing opposite to the saidsecond opening whereby, by holding said casing withits front opening facing a photographic scene, the mark being just readable by viewing said wedge through said second opening and mirror is characteristic of the scene brightness to be determined v,for a given average light condition, and a converting unit mqunted'upon the top wall of said casing adjacent to said second opening and comprising a firstadjustable scale member having a-series of exposuremarks thereon identical to those on said wedge and arranged to be set according to a mark read on said wedge, and a further relatively fixed scale member arranged in cooperative relation to the first scale member and' calibrated in coordinated exposure values.

6. In an exposure meteras claimed in claim 2, i

, a cover member hinged to the front edge of said second opening adapted to close said opening in the non-use condition of the meter and to be swung to a substantially vertical position to serve as a light shield in the operative position of the meter.

JOSEPH M. BING. 

